Method and apparatus for photographic scanning



R m A.

Marci 22, 1949.

H.L. COOKE METHOD AND APPARATUS FOR PHOTOGRAPHIC SCANNING l1 SheetsSheet 1 Filed Aug. 8, 1942 lNVENTOR H. 1.. COOKE ATTORNEYs March 22, 1949. CQQKE 2,464,793

METHOD AND APPARATUS FOR PHOTOGRAPHIC SCANNING Filed Aug. 8, 1942 I 11 Sheets-Sheet .2

INVENTOR H. L. Coo/(E ATTORNEYS 'A MIE; I

H. L. COOKE March 22, 1949.

METHOD AND APPARATUS FOR PHOTOGRAPHIC SCANNING 11 Sheets-Sheet 3 Filed Aug. 8, 1942 M ATTORNE m3 MQQ 11 Sheets-Sheet 4 H; L; 'cooKE" METHOD AND APPARATUS FOR PHOTOGRAPHIC SCANNING March 22, 1949.

Filed Aug. 8, 1942 March 22, 1949.

Filed Aug. 8, 1942 H. L. COOKE 2,464,793

METHOD AND APPARATUS FOR PHOTOGRAPHIC SCANNING ll Sheets-Sheet 5 INVENTOR BY MAC-06165 ATTORNEYS H. L. COOKE March 22, 1949.

METHOD AND APPARATUS FOR PHOTOGRAPHIC SCANNING Filed Aug. 8, 1942 ll Sheets-Sheet 6 o Vans INVENTOR ML. 600x45 BY A M TTORNEYS H. L. COOKE 4, METHOD AND APPARATUS FOR PHOTQGRAPHIC SCANNING 11 Sheets-Sheet 7 March 22, 1949.

Fil d Aug. 8, 1942 u l l k H. L. COOKE March 22, 1949.

METHOD AND APPARATUS FOR PHOTOGRAPHIC SCANNING Filed Aug. 8, 1942 ll Sheets-Sheet 8 OR COOKET Y 20-623, ATTORNEYS WNg H. L. COOKE March 22, 1949.

METHOD AND APPARATUS FOR PHOTOGRAPHIC SCANNING 11 Sheets-Sheet 10 Filed Aug. 8, 1942 INVENTOR 4 l. (00x5 BY I W/m v ATTORNEYS A! OMN ww v wmw QM MWN Patented Mar. 22, 1949 METHOD AND APPARATUS FOR PHOTO- GRAPHIC SCANNING Hereward Lester Cooke, Princeton, N. J., assignor, by mesne assignments, to H. Lester Cooke, Jr., Priscilla Cooke Stewart, and Russell Prickett,

as trustees Application August 8, 1942, Serial No. 454,108

24 Claims.

This invention relates to photographic scanning methods and apparatus. Its principal object is to provide a method of and apparatus for producing orthogonal photographic representations of objects or surfaces comprising portions of different elevation, which representations are free from errors or displacements due to parallax.

In the usual methods of taking photographs a camera is employed having a lens toward which the rays may be regarded as converging to a center. The photographic rays pass to the lens in the form of a cone and, due to the angularity of the rays with respect to the optical axis of the camera, there is a relative planimetric displacement of all features shown in the photograph which do not lie in any single datum plane of the object. All points of the object nearer to the camera than the datum plane show in the photograph as relatively displaced outward from the optical axis of the lens, while all parts of the object further from the camera than the datum plane are relatively displaced inward with respect to said axis. This is true of all photographs of solid objects taken in the ordinary way with any known form of camera, and thus it is impossible to use such a photograph as an accurate plan of the object, in which all the elements thereof are required to be shown in correct orthogonal relationship.

An outstanding example of the difiiculties involved in utilizing a photograph as a plan from whichmeasurements may be taken occurs in the case of photographs of terrain taken from airplanes, which it is desired to use as maps. Such photographs, even if taken from the highest altitudes at which it is practicable to fiy and take photographs, are subject to serious distortion, particularly if the photographs are of hilly or mountainous country, and it is therefore not feasible to use such photographs directly as maps or plans of the country. Accurate measurements cannot be taken directly from such maps. Numerous efforts have been made to correct airplane photographs so as to render them more available as maps, but all known methods of correction are only crude approximations and cannot take care of the intricate irregularities of the surface photographed.

In my application for U. S. Patent, Serial No. 328,175, filed April 6, 1940, Patent No. 2,309,752, dated February 2, .1943, I have disclosed a method of producing orthogonally corrected photographs of terrain and of preparing maps therefrom, which corrected photographs and maps are accurate within the limits of observable error,

although theoretically a slight deviation from exact orthogonal accuracy will be present. In general the method specifically disclosed in that case involves the preparation of a three dimensional scale model of the terrain or object photographed, the projection of the photograph on such model, and the rephotographing of the model with the projection thereon from a very long distance, approximating infinity, so that the cone of rays arriving at the camera from the model and producing the photograph is of exceedingly small angle. This reduces errors to a point where they are not objectionable and for practical purposes may be disregarded. For instance in the case of aerial photographs, it is possible to carve a three dimensional scale model of terrain shown in two over-lapping aerial photographs and then to rephotograph this model, with the photographic representation projected thereon, from a distance which would result in a photograph equivalent to one taken from an airplane flying 100 miles above the terrain represented. This produces a corrected photograph from which a map can be made which is accurate as to planimetry within the limits of measurable error. At the same time it is possible to use for photographing the model a very long focus lens, or telephoto lens system, which enables the corrected photograph to be made on a sufficiently large scale to preserve the detail of the original airplane photograph. The taking of very long focus photographs, however, as contemplated in my application for patent above referred to, involves certain practical objections, such as the necessity for a room or studio permitting the camera to be set up at a distance from the object photographed of perhaps to feet. It also involves an exceedingly solid mounting for the camera so as to avoid vibration effects, and the use of costly, long focus lenses,

Another method of producing orthogonally adjusted photographs is disclosed in my application for U. S. Patent, Serial No. 436,747. filed March 30, 1942, now abandoned. This method involves utilizing a telecentric lens interposed between the camera lens proper and the object, placed so that its principal focus is coincident with the outer nodal point of the camera lens, the two lenses being arranged coaxially. If the telecentric lens is of proper design and is co-extensive in area" with the object to be photographed, or with such part thereof as is to be photographed in a single exposure, it in effect transmits to the camera lens only rays leaving the object in directions parallel to the axis of the lens system, so that the photograph of the object is in effect identical with one photographed only by means of such parallel rays. While this method substantially eliminates the effects of parallax or perspective, it is subject to the limitation that the size of the object which can be photographed at one exposure can be no greater than the size of the telecentric lens employed. In the case of objects of considerable dimensions this difliculty might be obviated by shifting the camera laterally, without altering the orientation of its axis, photographing different portions of the object in succession, and then piecing these views together to form a connected whole. There are serious practical objections to this procedure. But if large objects are to be covered by single exposures very large telecentric lenses are required, which are costly, and which present serious problems of design and manufacture if the introduction of perccptible lens aberrations is to be avoided. It is also difiicult, if not impossible, to use a large telecentric lens to photograph a model of terrain while projecting a photograph of the terrain on the model, because the lens will distort the path of the projected rays.

In accordance with the present invention the objections to both of the methods above referred to are obviated. In the preferred embodiment the method employed is in a sense a modification of the procedure referred to above, viz. that of photographing the object in successive portions. But instead of photographing different parts of the object in separate operations and then piecing the resulting pictures together the method is employed of effecting continuous relative motions between the optical system, photographic plate and object in such a manner that the photographing of successive portions of the object is carried out as a continuous process and not as a step by step procedure. This relative mo-- tion is so effected as to cause the different portions of the photograph to appear in the form of a continuous picture on the plate, requiring no piecing of picture parts to achieve a connected photographic representation of the entire object. At the same time the theoretical errors due to conical projection involved in the process of the Patent No. 2,309,752, are avoided and it is possible to use a lens system of simple design and moderate dimensions which will produce an orthogonal projection accurate to within the limits of experimental error. The apparatus used is compact and efficient and can readily be constructed to produce orthogonally corrected photographs of objects of any reasonable size.

Stated broadly the present invention embodies a process and apparatus for photographically scanning the object to be represented. The object, photographic plate, and the camera, equipped, in one form of apparatus, with a telecentric optical system, are maintained by coordinated motions of one or more of these elements in such relation that a point to point orthogonal correspondence between elements of the object photographed and corresponding elements of the plate on which the image is recorded is maintained continuously during the process of exposure, and in this Way it is possible to produce a continuous exposure on a single plate covering an area of much greater extent than that included in the instantaneous field of view of the optical system employed. If the movements are so carried out that the optical axis of the system is maintained normal to the fixed plane of the photographic plate, orthogonal projections of large objects or areas may be obtained. The elimination of errors due to parallax may be substantially accomplished even without the use of a telecentric system because it is possible to employ an optical system having a very small field of view, so that the area photographed at any instant subtends a cone of rays of very small angle. The rays passing from the object to the camera lens at any given instant may therefore be treated as substantially parallel to each other and to the optical axis of the system. The progressive scannning of the object in this way permits an area of any reasonable extent to be photographed in continuous orthogonal projection.

In the preferred embodiments of my invention I combine the use of a telecentric optical system with scanning apparatus such that a photograph is produced in which parallax is wholly eliminated, the only remaining errors being those due to imperfection of lenses and mechanical construction of the apparatus. Since the field of view of the optical system is restricted to a small angle the imperfections and aberrations of the lenses produce no detectable errors in the photograph. Also the apparatus is such as to lend itself readily to precision methods of manufacture. Thus the residual errors of the process may readily be made too small to be detected.

While my invention is of broad application to the photographing of objects, it is especially applicable to the production of planimetrically corrected photographs and photographic or phototopographic maps of terrain from which all effects of parallax, or perspective, have been eliminated. By the use of a scanning apparatus as described which has a small objective covering at any instant only a very small part of the model to be photographed, it is possible to photograph a model of the terrain while the same has the original photograph projected on it. The movable scanning element is so arranged and operated as not to interfere with such projection, and thereby enables the production of a planimetrically adjusted photograph of the terrain, equivalent in all respects to the original photograph thereof, except that it has been orthogonally corrected.

In some embodiments of my apparatus it is also possible to adjust the scale of representation as a part of the photographic scanning process, thus making it possible to produce any desired reduction in scale of the corrected photographs so as to make them suitable for direct employment in ordinary enlarging and map drawing projectors. Of course the scanning apparatus could also be arranged to produce an enlarged photograph if desired, but it is in most cases convenient to produce a reduced photograph. The scanning apparatus is compact and can be made practically automatic in operation.

In the accompanying drawings in which certain preferred embodiments of the invention are chosen to illustrate the principles thereof Figures 1 and 2 are diagrams illustrating the general principle of operation of the invention.

Figure 3 is a diagram showing how distortions due to parallax are reduced by diminishing the field of view of the lens.

Figure 4 is a diagram showing the use of a telecentric system for production of an orthogonal photograph of the same dimensions as the object.

Figure 5 is a diagram showing how an orthogonal photograph may be produced with reduction of scale by moving the plate as w ell as the scanning optical system.

Figure 6 is a diagram showing the use of a telecentric system with reduction of scale, and without the use of an image erecting system.

Figure 7 is a diagram similar to Fig. 6 but showing the effect of introducing an image erecting system.

Figure 8 is a pair of diagrams, A and B, showing two alternative paths of the scanning system over the object.

Figure 9 is a rear elevation of a practical embodiment of the apparatus suitable for photographing any object of which it is desired to produce an orthogonal photograph, the moving parts being shown in the positions which they occupy at the beginning of the scanning operation, and certain parts being indicated in dotted lines in subsequent positions.

Figure 10 is a plan view of the apparatus shown in Fig. 9.

Figure 11 is a horizontal section of a part of the apparatus taken on line ll-Il of Fig. 9.

Figure 12 is a vertical transverse sectional view taken on line l2l2 of Fig. 11.

Figure 13 is a similar view taken on line l3-l3 of Fig. 11.

Figure 14 is a fragmentary rear elevation of the apparatus showing the optical frame and carriage at the beginning of a scanning path, the lens tube being shown in vertical section.

Figure 15 is a view similar to Fig. 14 showing the optical frame and carriage at the end of a scanning path.

Figure 16 is a view in transverse vertical section through the end of the optical tube nearest to the object showing the telecentric lens and its adjustable aperture mask.

Figure 17 is a horizontal sectional view on line ll-ll of Fig. 16 showing the mask.

Figure 18 is a diagram showing the overlapping of the mask positions during two successive scanning paths.

Figure 19 is a diagram similar to Fig. 18 showing a diiierent shape of mask.

Figure 20 is a diagram similar to Figs. 18 and 19 showing still another shape of mask.

Figure 21 is a fragmentary elevation showing an adjustable aperture mask which may be used at the end of the optical system adjacent to the plate, in place of the mask equipment shown in Figs. 16 to 20 inclusive.

Figure 22 is a diagram showing parts of the machine in rear elevation and illustrating the -motor reversing mechanism, reversing and safety switches, and electrical connections.

Figure 23 is a diagrammatic view in end elevation showing a modified form of apparatus, particularly suitable for the photographing of models of terrain under a projection apparatus such as a series of Multiplex projectors, the Multiplex apparatus also being shown.

Figure 24 is a plan view of part of the modified form of apparatus shown in Fig. 23.

Figure 25 is a rear elevation of the apparatus shown in Fig. 23.

Figure 26 is a transverse vertical section on line 2626 of Fig. 25.

, Figure 27 is a longitudinal vertical section on line 2'l2l of Fig. 24.

Figure 28 is a perspective view from the front showing parts of the optical system, and the carriage and front track for the same.

Figure 29 is a transverse vertical section on line 29-29 of Fig. 27 showing the optical system.

Figure 30 is a longitudinal vertical sectional 6 view on line 30-30 of Fig. 29 showing a part of the image erecting prism system.

Figure 31 is a perspective diagram of the image erecting prism system.

Figure 32 is a diagram showing a series of Multiplex projectors illuminating a model of terrain and indicating how the casting of shadows on the model by the scanning tube is avoided, and

Figure 33 is a wiring diagram showing the mode of illuminating the projectors at the proper times and in proper sequence.

Figure 1 shows the principle of the invention in the simplest form required to produce a photograph of an object a, b, c, by means of a lens I having a field of view included within the solid angle 0, this field not being of suificient size to cover the entire object. In order to photograph the entire object, a, b, c, the lens is moved progressively over the object to the position I. The image will appear in inverted position a b c on the photographic plate 2, and by progressively moving the plate, in continuous synchronism with the movement of the lens but at double the speed, to the position 2, a point to point correspondence between elements of the object and corresponding elements of the image on the plate is maintained throughout the exposure. Thus the image position b of the point I) will move to the position b" as the lens and plate move in synchronism from positions I, 2 to positions I, 2'. The image a of the point a as recorded on the plate at the beginning of the exposure will move to the position a where it will be out of the field of the lens, and at the'end of the scanning operation the image of the point 0 will be recorded on the plate at c. All the intermediate points will be similarly recorded as the lens and plate travel. In Fig. l the distances between the object and lens, and between the lens and the plate are equal and the image will be the same size as the object. The plate will thus have to be moved at twice the speed of the lens, the object remaining stationary.

Since the eiiect produced depends on motions changing the relative configuration of the lens, the plate and the object, it is obvious that any combination of motions of these three elements which will result in the same change in relative configuration will accomplish identical results. Thus the plate may be maintained stationar and the object moved at twice the speed of the lens, in the same direction; or the lens may be maintained fixed and the plate and object moved with equal speeds in opposite directions. The same principle holds true throughout this specification in all cases where relative motion, between lens, plate and object is specified. as any combination of motions of these three elements which will result in the same change in relative configuration may be substituted for the combination of motions specified.

Figure 2 shows the effect of introducing into the system an image erecting optical device, such for instance as a pair of erecting prisms. The presence of such an image erecting device is indicated conventionally by the S-shaped arrow 4 passing through the lens. With such an optical system it will be seen that the image will remain stationary as the lens and erecting system are moved as a unit. so that both the plate and the object will remain stationary if the lens is half way between the object and the plate and a full size photograph of the object is made. This appears by considering for instance the ray leading from the point b, through the lens and erecting 7 system to the image point b. The image of the point 1) remains stationary on the stationary plate at 12' throughout the scanning movement between the two indicated positions of the lens with erecting system.

Figure 3 illustrates the effect of scanning with a lens system covering a very small field of view as compared with the use of a lens system covering a large field. For instance, if it is desired to photograph on plate 2 a model of terrain 3, this may be done by scanning the model with a lens I covering a small field of view, the system being shown as also provided with an image erecting system indicated by the arrow 4. One-half the field of view is indicated by the angle ,8. For purposes of comparison a large field of view, such as would be required if a lens were used adapted to cover the whole or a considerable part of the model, is also indicated, half of such field of view being indicated by the angle [3. If the model were photographed with a lens including the wide field of view it will be seen that large errors in planimetry would appear in the photograph on plate 2. For instance, if a point r, a considerable distance above the datum plane D of the model, were photographed, such point would appear at r on the plate, whereas it would appear at the point r" if the photograph were correct in planimetry. The distance between T and 1-" would thus represent the displacement error of the image of the point r in the photograph. However, if only a small field of view is covered, indicated by the angle e, the displacement of the point p, for example, would be so slight as to be negligible and the point p would appear on the plate at p in approximately the correct position. The same would be true of all points photographed by the lens of small field of view as it moved across the object being scanned. Thus with a sufiiciently small field of view difierences in elevation of the points on the object would not result in displacement errors of measurable amount. By scanning the object with a lens of small field, therefore, a photograph substantially accurate in planimetry can be secured without making the distance from the object to the plate excessive or using extremely long focus lenses.

Fig. 4 shows how an object may be scanned by the use of an optical system including a telecentric lens 5. In this system the telecentric lens 5, camera objective I, and image-erecting system indicated by the arrow 4, are mounted on a common support or optical tube '6 which can be moved normal to the axis of the system so as to scan the object or model 3. The principal focus of the telecentric lens 5 coincides with the outer nodal point of the lens I, the two lenses being arranged coaxially. Lenses arranged with respect to each other in this manner will be referred to as in telecentric relationship. With the telecentric lens 5 and camera objective I in such specified relationship any ray passing from an element of the object 3 to the telecentric lens 5 in a direction parallel to the common axis of the two lenses will be refracted by the lens 5 so as to proceed toward the outer nodal point of the lens I, and will subsequently proceed along a parallel path, intersecting the inner nodal point of the lens I, till it reaches the plate 2. If the optical system is properly focused on the object 3 a clear image of the said element of the object 3 will be formed where the above specified ray meets the plate 2. In dealing with telecentric systems in adjustment as specified above. rays which in their passage between the object and photographic plate pass along lines directed toward and away from the nodal points of the camera objective will be referred to as nodal rays. Such rays are marked with arrowheads in Fig. 4. Consideration of this figure will show that the nodal rays from the points p and q on the object 3, irrespective of the distances of these points from the datum plane D, project orthogonally on an imaginary plane JJ passing through the lens 5, normal to its axis, at the points page. The objective I projects a scale reproduction p'q' of the points mm on the plate 2. Since puqo forms an orthogonal projection of pq, and since pq' is a scale reproduction of poqo, it follows that pq' is a scale orthogonal projection of pq taken parallel to the ommon lens axis. The scale of this projection pq' is directly proportional to the ratio of the distances of the plate 2 and telecentric lens 5 from the objective I. This general condition holds true for all telecentric systems referred to in this specification. Rays other than nodal rays passing from any single element on the object 3 through the lenses 5 and I and brought to a focus on the 'plate 2 will focus at the same point as the nodal ray originating from the same element. Thus it is seen that the nodal rays determine the image positions of elements from which they originate and other rays radiating from these elements and brought to a focus on the plate meet the plate at the same points as the corresponding nodal rays, so that their main function may be regarded as that of augmenting the intensity of the image formed by the nodal rays.

Returning now to Fig. 4 it will be seen that the images p and q of points p and q, for instance, appear in correct planimetric position on the plate irrespective of the relative elevations of points p and q. In the system shown in Fig. 4 the distance d from the telecentric lens 5 to the camera lens I is equal to the distance d" from the camera lens I to the plate 2. The image on the plate 2 will thus be of unit magnification, and the images of all elements of the object 3 will remain stationary on the stationary plate 2 as the lens system is moved to scan the object. Thus with the arrangement shown in Fig. 4 both object and plate will remain stationary, and only the optical system will have to be moved.

Fig. 5 shows how a photograph of an object 3 of any desired scale may be produced as a part of the scanning operation. In the example shown, the distance d from the object to the lens is made three times the distance d from the lens to the plate, so that there is a reduction in the size of the image of 1:3 such ratio being designated by l/N. In this arrangement an image erecting system is employed, as indicated by the S-shaped arrow 4. In the case of such a change in scale in photographing a fixed object 3 it is necessary to'produce relative motion between the optical system and the plate so as to maintain a point to point correspondence between elements of the object and the images of such elements, in fixed positions with respect to the moving plate 2. It may be shown theoretically that if the scale of reduction of the image is to be l/N, in order to prevent movement of the image with respect to the plate, when an image erecting system is employed the plate and the optical system must be moved in the same direction through distances in the ratio (1l/N) :1, whereas when no image erecting system is employed the ratio of corresponding displacements must be (l-I-l/N) :1. In the arrangement shown in Fig. 5, since N=3 it 9 follows that for each displacement of the optical system the plate must be given a corresponding displacement two thirds as great, in the same direction. Under these conditions the image on the plate 2 of any element of the object 3 will maintain a fixed position on the plate 2, and thus may be recorded photographically without blurring.

Figures 6 and '1 show how scanning systems, including telecentric lenses, may also be used to produce photographs at a different scale from full size. In both instances depicted the distance d from the telecentric lens 5 to the camera lens I is three times the distance d from the camera lens I to the plate 2. Thus in both cases the reduction in scale, l/N, is 1:3. Fig. 6 shows an optical system without image erection, while Fig. '1 shows the effect of introducing an image erecting device. If there is no image erection, as in Fig. 6, then the plate must move faster than the optical system, in the ratio 4:3, while if there is image erection, as shown in Fig. I, then the plate does not have to move as fast as the optical system, the ratio of the two speeds being 2:3. In the first case the ratio of the distance moved by the plate to the distance moved by the optical system is (1+1/N) :1, while with erection of the image the relative distance moved by the plate and optical system is represented by the ratio (1-1/N) :1.

In scanning objects of any considerable size it is usually not possible to cover the entire width of the object with a single travel of the optical system across the same. Accordingly the object is scanned in strips. Fig. 8 shows two methods of accomplishing this. In the diagram A the optical system travels across the strip C from right to left. The system is then rendered inactive by closing a shutter, turning off lights, or otherwise, and is moved back to the right hand side of the object, and then moved downward a distance equal to the width of the strip and the object is then again scanned from right to left, and so on until the entire surface of the object is covered. Diagram B shows an alternative mode of operation in which the optical system is moved from right to left, then down a step and fromleft to right, then down another step, and so on. In this instance it is not necessary to close a shutter or perform any equivalent operation.

It should be noted that if the reduction in scale of the photograph is to be 1:N and an image erecting system is employed. then in the lateral movements, left to right and back again, shown in A and B, Fig. 8. the ratio of the speed of motion of the plate to that of the optical system must be (1-1/N):1, and also the amounts of transverse displacement, parallel to the arrows w. between the photographing of strips such as 0 must be in the same ratio, (11/N) :1, for the amount of displacement of the plate compared with that of the optical system. If no erecting device is employed the ratio of the corresponding motions is (1+1/N) :1.

General Purpose Photographic Scanner In Figs. 9 to 22 inclusive, a practical embodiment of a scanning camera is illustrated. This design is specially adapted for scanning an object of which it is desiredv to make an orthogonal photograph, such for instance as a piece of machinery or mechanical object, diagrammatically represented at A, which may be mounted on any suitable stationary support such as B, Figure 9. The scanner is arranged to operate in a vertical 10 plane, and, as illustrated, is not provided with an image-erecting optical system, although it could be modified for use with such a system if desired. The instrument as shown is constructed to make a reduced photograph of the object on a scale ratio of 1 to 4. While the instrument is illustrated as arranged to photograph the object as projected on a vertical plane, it could readily be mounted so as to operate in a horizontal or any other position desired.

The scanner comprises a bed plate I00 mounted on feet IOI and carrying a pair of upright standards I02 and I03 at its ends. The bed plate also carries an electric motor I04 provided with reversing control mechanism indicated at I05 (Figs. 10 and 22) The standards I02 and I03 support, and are connected by, an upper horizontal guide rod I06, and a lower horizontal guide rod I01. A frame I08, on which is mounted the carriage for the optical or lens system of the camera, and which will hereinafter be referred to briefly as the optical frame, is mounted to slide on the rods I06 and I01. The frame has an open center, as indicated at I09 and has bearing sleeves H0 and I I I sliding on the rod I06, and bearing sleeves I I2 and H3 sliding on the rod I01. The frame I08 also carries a pair of vertical guide rods H4 and H5 on which is mounted the vertically movable carriage II6 which carries the optical system of the camera and will be referred to briefly as the optical carriage. The carriage II6 has perforated lugs H1 and H8 which slide on the rods H4 and H5 respectively. The rod H5 is shown as square and provided on one face with spaced notches I I9, for a purpose which will be explained below. Mounted in an opening I20 (Fig. 11) in the carriage H6 is the camera objective lens mount I2I. The objective I22 may be of any suitable type, such as a high grade anastigmat, and is not therefore illustrated in detail. Fixed to the lens mount is a tube I23 which projects horizontally toward the object to be photographed, and carries at its outer end a telecentric lens I 24. (Figs. 10 and 16.) The principal focus of the telecentric lens I24 coincides with the outer nodal point of the camera objective I22, so that the only rays passing toward and away from the nodal points of the camera lens I22 in their passage to the plate I25 are rays which leave the object in substantial parallelism with the optical axis of the lens I22. Projecting from the rear of the lens mount in the direction of the plate is a tube I26.

A second frame I21, hereinafter referred to as the plate frame, is mounted to slide on the rods I06 and I01. This frame has an open center as indicated at I26, and is provided with bearing sleeves I29 and I30 sliding on the rod I06, and with bearing sleeves I3I and I32 sliding on the rod I01. The frame I21 carries a pair of vertical guide rods I33 and I34, the latter being shown as of square sect on and provded on one face with notches I35 for a purpose to be described below. Mounted to slide vertically on the rods I33 and I34 is the plate carriage I30 which has lugs I31a and I311), 138a, and I381) through which the guide rods I33 and I34 pass respect vely. The

in Figs. 11, 12 and 13, this is accomplished by the use of a flexible bag or bellows I42. While the optical frame I08 and the plate frame I21 both slide longitudinally on the rods I06 and I01, it will be noted that there is room for the frame I21 to move relatively to the frame I 08 within the space between the bearing sleeves H and III, H2 and H3, of the frame I00.

For driving the frames I08 and I21 longitudinally, a pair of feed screws is provided, screw I43 engaging the half nut I44 on the frame I08, and screw I45 engaging the half nut I46 on the frame I21. In the machine illustrated, the optical system is provided with no image-erecting device, so that the plate frame I21 must move at a faster rate than the optical frame. This differential movement may be secured by any suitable gearing, but as illustrated is accomplished by making the pitch of the screw I45 greater than the pitch of the screw I43 in the ratio of to 4, i. e., (1+1/N) :1. The two screws are driven at a uniform angular speed, this being shown as accomplished by intermeshing similar gears I41 and I48 on the respective screws I43 and I45, the screw I45 extending beyond the end frame I02 and carrying a pulley I49 driven by a belt I50 from the electric motor I04. One of the screws has a right hand thread, and the other a left hand thread, as shown.

The optical carriage I I 6 is fed vertically on the guide rods II 4 and II5 of the optical frame I08 by means of a reciprocating feed rod I 5I which is provided on one face with transverse notches I52 (Fig. 13). The rod I5I is mounted for limited vertical reciprocating motion in aligned holes in the lugs I53 and I54 at the bottom and top, respectively, of the optical frame I08. The rod I5I also passes through openings in the lug II8 on the optical carriage. The upper lug II8 on the optical carriage II 6 has a transverse hole in it through which slides the pawl I55 which has a downwardly facing wedge shaped end I56 adapted to engage the notches I52. The pawl I 55 is normally pressed towards the bar I5I by a spring I51 mounted in a recess in the lug H8 and it may be manually retracted against the pressure of the spring by a knurled head I58. The lug I I8 also carries a second pawl I 59, similar to pawl I55, adapted to engage the notches H9 in the square guide rod II5. (Figs. 9 and The reciprocating feed rod I5I is normally in down position, as shown in Figs. 9 and 13, to which position it is urged by gravity assisted, if necessary, by a spring I60. At the end of every scanning travel of the frame I08 (to the left in Fig. 9) the rod I5I, which has on its lower end a roller I6I, engages a cam I62 which is'adjustably mounted on a rail I63 supported between the standards I02 and I03. The cam may be locked in any desired position on the rail by the set screw I64. When the frame I08 reaches the left end of its travel the roller I6I' rolls up the cam I62, thus lifting the rod I5I, which carries with it owing to the engagement of pawl I55 in a notch I52, the optical carriage II6. As the carriage moves up, the tooth on the pawl I59 slides out of a notch in the guide rod H5 and moves up into engagement with the next higher notch in the guide rod. The carriage is thus firmly held in its raised position. When, due to reversal of the motor I04, the frame I08 starts its return movement to the right, the roller I6I slides off the cam I62 and the feed rod I5I moves back to its original position, the pawl I55 snapping out of the lower notch on the feed rod I5I into the 12 next higher notch thereon, ready for the next feeding step which takes place at the end of the next reciprocation of the frame I08 to the left. In this way it will be seen that every time the frame makes a complete reciprocation, the optical carriage is raised through a distance of one notch on the guide rod II5. As the notches may readily be cut with high precision an accurate step by step feed of the carriage is thus provided. At any time it is desired to return the carriage to a lower position this may be accomplished by merely retracting the pawls I58 and I59 by hand and sliding the carriage down.

The means for producing step by step vertical feed of the plate carriage is in all respects similar to that described for feeding the optical carriage, except that the notches in the guide and feed rods are spaced further apart than the notches in the rods H5 and I5I. This greater spacing of the notches provides for greater upward movement of the plate carriage, which is in the same ratio to the corresponding upward movement of the optical carriage as the ratio between the longitudinal movements of the plate frame and optical frame respectively, viz., (1+1/N) :1. The plate frame carries a reciprocating feed rod I65 corresponding with the optical carriage feed rod I5I, with feed notches as shown at I66, and the carriage guide lug I38a carries a feed pawl I01 engaging with the notches I66, and a holding pawl I68 engaging with the notches I35 in the face of the square guide rod I34. The plate carriage feed rod I 65 is slid-ably mounted in lugs I69a and l69b on the plate frame and is urged downwardly by gravity and by the spring I 10, and carries at its lower end a roller I1I which is adapted, at the left hand limit of travel of the frame I21, to ride up on a cam I12 which is held in adjustable position on the track I13 by a set screw I14. The cams I62 and I12 are set in adjusted positions upon their tracks, dependent upon the length of scanning travel of the frames necessary to cover the size of object being photographed.

With the arrangement described it will be seen that the rotation of the feed screws I43 and I45 will cause the optical and plate frames to move to the left so as to cause the telecentric lens I24 to sweep in a horizonta1 path from right to left across the object. At the same time the plate frame is moved from right to left but at a higher speed in the ratio (1+1/N) :1, so that when the telecentric lens reaches the left hand end of the object, the plate will have moved from its initial position where its left hand edge was opposite the axis of the optical tube I26, to a position in which its right hand end is opposite the axis of such tube. Thus a horizontal strip of the plate has been exposed from left to right while the telecentric lens has scanned the object from right to left. Since with the optical system shown the image is inverted, this opposition of operations is necessary if a point to point correspondence between elements of the object and corresponding elements of the image on the plate is to be attained. Under the conditions specified, with the camera focused on the object, a sharp image will be formed on the plate, and this image will be stationary with respect to the plate during all phases of the exposure. At the end of each scanning stroke the rollers on the lower ends of the carriage feed rods engage their respective cams, thus lifting the optical and plate carriages through distances of one notch on their respective feed rods. This will feed the plate carriage l v A ll slightly more each time than the optical carriage, in the ratio of (1+1/N) :1, so that when the telecentric lens reaches its last scanning position adjacent to the top of the object, the plate will have moved up to a position as indicated in dotted lines I M in Fig. 9, in which the lower edge of the plate is aligned with the axis of the optical tube I26. Thus the entire plate has been exposed when the entire object has been scanned, and the inverted photograph covers the whole plate (or such part thereof as it is necessary to use.)

In the machine as illustrated exposure of the plate is made only during the travel of the frame from right to left. This has the advantage of .avoiding possible errors due to backlash in the mechanism, which might be present if the exposures were made in both directions of travel. The latter arrangement is possible if provision is made to avoid all backlash and if the construction is such that the carriages will be fed an upward step at each end of the reciprocatory travel of the frames. However the machine as shown is simpler and easier to construct with satisfactory accuracy. With such single directional scanning it is necessary to prevent exposure of the film during the return travel of the frames from left to right. This is accomplished in the construction illustrated by providing a shutter I15, Fig. 15, which may be of any suitable type, such as the diaphragm shutter indicated. The shutter may be operated in any suitable manner, as for instance by the cable release I16, the end of which is shown as attached to an activating rod I11, Figs. 14 and 15, slidably mounted in the optical frame I08 and carried therewith. The lower end of the rod I11 carries a roller I16 which engages with the cam I62. In this arrangement when the roller I18 rolls up the cam I62 it actuates the cable release I16 so as to trip the shutter, causing the same to close, as shown in Fig. 15, and the shutter will remain closed until the frame reaches the right hand limit of its travel. At that time it is desired to open the shutter, and this is accomplished by providing a cam I19, Fig. 9, mounted on the track I63, with which the roller I18 engages. The cable release I16, preferably of the well known antinous type, is so constructed that successive depressing of the roller I18 at the end of the cable w ll cause the shutter to open and close alternately. The shutter is so set that when the cable release is operated by the roller I18 riding up the cam I19 the shutter will be opened and will be closed when the roller I18 rides up the cam I82, Fig. 10. In this way successive strips of the plate are exposed as the frames I08 and I21 travel to the left, Fig. 9. whereas no exposure occurs on the return trip of the carriages. the shutter then being closed.

It is possible to control the motor by hand switches and to reverse the feed of the screws either by reversing the motor directly or by means of any suitable reversing mechanism. However it is desirable to make the machine automatic in operation as far as possible. and suitable controls for this purpose are indicated. The motor I04 is shown as of a type which may be reversed by shifting the position of the brushes IBI (F g. 22) The reversal is accompli hed by means of a solenoid I82, thearmature I83 of which is connected by suitable linkage to a brush carrying reversing ring I84. Whenever the solenoid is not energized the brushes are held in the posit on shown in Fig. 22 by the spring I85 and whenever the solenoid is energized the brushes are shifted so as to reverse the rotation of the motor. The main reversing switch I86, Figs. 9 and 13, in the solenoid circuit, is shown as mounted on the lug I53 on the optical frame I08. When the frame reaches the left hand limit of its travel the switch engages a stop I81, Fig. 15, which is shown as attached to the cam I62. This engagement causes the switch to snap over and starts the reverse travel of the frames. When the frames reach the right hand position, the switch I86 engages a stop I88, Fig. 9, adjacent to the cam I19 which again reverses the motor and starts the frames on a new scanning stroke. As a safety precaution it is desirable to provide safety switches I89a and I89b, Fig. 9, at the limits of the maximum stroke of the apparatus. These switches are interposed in the motor circuit and in the event that the reversing switch I86 should fail in its operation for any reason, one or the other of them would be engaged by the frame, depending upon the direction of its travel, so that the motor circuit would be positively broken and travel of the carriage stopped before injury to the apparatus could occur. A similar safety switch I890 is preferebaly provided near the top of one of the frames, as for instance the frame I21, where it would be engaged by the plate carriage I36 when it reached th upper limit of its movement, thereby postively stopping any further feed.

The motor circuit is preferably provided with a rheostat I90 or other suitable means for regulating the speed of travel of the frames and carriages. It is important to provide some regulating means for this purpose, as the exposure of the photographic plate is determined by the speed of travel of the optical system over the plate as well as the limiting aperture of the optical system such as the iris diaphragm of the shutter I15.

During the scanning process the plate is exposed in successive longitudinal strips. As the optical system moves over the plate at a uniform speed throughout each strip no difficulty is experienced in securing a substantially uniform and unbroken exposure throughout each strip. In order to secure a satisfactory effect in the finished photograph, however, it is desirable to have the successive strips joined accurately, so that they do not on the one hand overlap resulting in an over-exposed strip, or on the other leave an under-exposed line between them. For adjusting the line of juncture between successive strips it is hexagon.

desirable to use an adjustable mask placed adjacent to the telecentric lens. Such a mask is shown at I9I in Figs. 16 and 17, and comprises two mask plates I92a and H321) mounted to slide in a frame I93. Adjusting screws I94 may be pro vided for securing accurate adjustment of the mask plates. The avoidance of any visible line between successive strips is facilitated by shaping the mask plates in such a way as to provide adjacent overlapping areas of partial illumination. Figs. 1''! and 18 show a preferred form of mask for accomplishing this purpose, each of the plates having a pointed notch I95 therein so that the mask opening is in the general form of a The mask is so adjusted that the distance between the apex of one notch and the base of the other notch is equal to the lateral displacement of the optical carriage II6 between successive reciprocating motions in photographing successive strip areas of the object. here is an overlap represented by the distance 10 between the successive strips, this overlap being only partly exposed at each travel of the optical system so that the combined exposure on this region of penumbra due to successive photographing of adjacent strips of the object will be uniform and exactly equal the normal exposure permitted by the portion of the mask opening of maximum width, so that a substantially uniform exposure throughout the entire photograph will be secured.

Instead of the shape of the mask shown in Fig. 18 other shapes may be used, accomplishing a similar result, such as the trapezoidal shape shown in Fig. 19, or the shape with oppositely inclined ends shown in Fig. 20. Other shapes accomplishing a similar result may of course be employed.

In some designs of the apparatus the mask shown in Figs. 17 and 18 is preferably omitted and in its place the optical tube 126 nearest to the plate is provided with an aperture mask and this may desirably be made adjustable as illustrated for instance in Fig. 21. The construction here illustrated comprises a base plate 196 having a large opening 19'! therein, which carries two longitudinally adjustable notched masked blades 198 and two laterally adjustable straight blades 199. In order that the masking device shown in Fig. 21 should control the area of exposure in the same manner as the arrangement described in connection with Figs. 16, 1'7, 18, 19 and 20 it is merely necessary that the shapes of the openings in the masks should be identical, with the linear scale of the dimensions of the opening in the mask shown in Fig. 21 reduced in the ratio :N as compared with the opening effected in accordance with Figs. 16, 17, 18, 19 and 20.

When adjusted as hereinbefore specified the devices shown in Figs. 16 and 17 and that illustrated in Fig. 21 will produce identical results, with regard to exposure, when employed in photographing an object. It is worthy of note that if the masking device shown in Fig. 21 is employed it should be located as close as possible to the photographic plate.

Relief photograph scanner In Figs. 23 to 33 inclusive, a scanning camera of modified construction is illustrated which is especially adapted for photographing objects placed on a horizontal support or table. The construction is particularly designed for the photographing of relief models of terrain while under projection apparatus such as the wellknown Multiplex equipment. The general arrangement of the apparatus when used in connection with the Multiplex projectors is illustrated in Fig. 23 in which 200 is a table on which are mounted the standards 201 carrying the longitudinal supporting bar 202 of the usual Multiplex apparatus. Adjustably supported by the bar 202 are a plurality of Multiplex projector heads 203 only one of which can be seen. The relief model 204 of terrain to be photographed rests on the table 200 under the projectors so that one or more of the aerial diapositives placed in the projector heads may be projected upon and in registry with the model. As in the Multiplex apparatus the projector heads are set up in positions corresponding to the positions of the cameras at the time the photographs were taken, the photographs are projected upon the model from positions corresponding to the scale of the model, with the positions from which the photographs were made, and exact correspondence between the photographs and the relief of the model can be secured. The scanning camera is shown at 205 and may conveniently be mounted on a stand 206 which may be moved into juxtaposition to the Multiplex apparatus. In this embodiment of the scanner, the optical and plate frames and carriages move in horizontal planes, and the optical tube 20! carrying a telecentric lens 208 projects laterally beneath the Multiplex projector heads and over the model. This construction enables the scanner to be used without interference with the Multiplex apparatus, as the only part of the scanner which extends into the field of the photographs projected by the Multiplex is the optical tube 201 which can be made of small dimensions so as to cast a very narrow shadow as it moves over the model. The general construction and operation of this type of scanner is similar to that already described with such changes as are necessary to adapt it to operation in a horizontal plane. This scanner is also shown as embodying an image erecting optical system, although this is not essential, as it could be made to operate without erecting the image.

The scanner comprises a frame including a bed plate 209 carrying uprights 210 and 211 to which are attached longitudinally extending horizontal rails 212a and 212b for carrying the plate frame, and 213a and 21319 for carrying the optical frame.

The plate frame comprises a pair of transverse frame members 214a and 214b, connected by the end pieces 215a and 2151) (Fig. 24). Rails 216 and 211 are rigidly attached to the frame members 214a and 214b. The rail 212a, as shown, has a V-shaped upper edge and the lower surface of the end piece 215a is grooved to engage it. The other rail may be similarly V-shaped, but is more conveniently made flat and engaged by a flat surface on the frame member 21512. The transverse frame members 214a and 2141) are provided with transverse track flanges 211i and 211, the upper edges of which are made true so as to constitute tracks for the plate carriage 218. The track fiange 211 as shown, is provided with a V-shaped upper edge, while the other track flange 216 has a fiat edge, the plate carriage 218 having downwardly extending flanges 219a and 21% (Fig. 25) resting on said track flanges 216 and 211. The plate carriage 218 has a central opening above which is mounted the plate or film holder 220 which is retained in the frame 221 rigidly fixed to the plate carriage. The plate carriage has brackets 222 which carry rollers 223 engaging the under surfaces of ribs 224 on the track flanges 216 and 211, said rollers being preferably pressed upward against such surfaces by spring 225 supported by adjusted screws 226.

Mounted on the lower pair of longitudinal rails 213a and 213i) is the optical frame which comprises the transverse frame members 221a and 2211) which are connected by the end pieces 220a and 22817. The transverse frame members 221a and 22lb are provided with transverse track flanges 229a and 2291) on the true upper surfaces of which slides the optical carriage 230. The optical carriage is preferably provided with a pair of retaining rollers 231 mounted on a bar 232 which is urged upwardly by a pair of springs 233, supported on adjusting screws 234. The rollers engage under ribs 235 formed on the flanges 229a and 22%. By adjusting the screws 234 the pressure of the rollers against the ribs may be varied so as to regulate the pressure of the optical carriage against its tracks.

Suitable mechanism is provided for feeding the plate and optical frames longitudinally on their respective rails, 212a and 2121), 213a and 213b. As illustrated, particularly in Fig. 25, the

feeding means comprises a pair of lead screws 236a and 236b, one of which is left handed, said screws being linked together by meshed gears 231 and driven by the pulley 238 and belt 239 from an electric motor 240. An arm 24! projects from the plate carriage 2 i 8 and carries a nut 242 which engages the thread on the screw 236a while the optical carriage 230 carries a nut 243 which engages the thread of the screw 23Gb. As this construction is provided with an optical imageerecting device it is necessary for the optical frame to travel faster than the plate frame, so the screw 23Gb is made of greater pitch than the screw 236a, in the ratio l:(1-1/N). For feeding the plate carriage 2| 8 transversely of the machine on the tracks of the plate frame suitable feeding means are provided which are illustrated as comprising the feed rod 244 provided in its upper surface with notches 245 which are adapted to be successively engaged by a pawl 246 slidably mounted in a bracket 241 on the side of the plate carriage and yieldingly pressed towards the feed rod by a spring (not shown). The feed rod is mounted for limited endwise reciprocating movement in openings in lugs 248a. and 2481; on the plate frame On one end of the rod 244 is mounted a roller 249 which is adapted to engage with a cam 250 adjustably mounted on the cam track 25I secured to the frame uprights 2). At the other end of the feed rod 244 is a spring 252 which urges the feed rod to its retracted position when the roller. 249 is not in engagement with the cam 250. The action of the feed rod, the cam and the pawl on the plate carriage is similar to that described in connection with the embodiment of the machine shown in Figs. 9 to 22. However, as the travel of the carriage is in a horizontal plane, it is not necessary to provide a holding pawl for engagement with notches in a fixed member, but the carriage will stay in the position to which it is moved by the feed rod. The friction on the tracks, increased to such extent as may be necessary by the pressure of the spring pressed rollers 223, prevents accidental displacement of the carriage.

For feeding the optical carriage 230, Fig. 28, along the tracks on the optical frame, a reciprocating feed rod 253 is provided, similar to the feed rod 244. The notches 254 in the feed rod 253 which are engaged by the spring controlled pawl 255 mounted in the bracket 256, are spaced further apart than the notches 245 in the plate carriage feed rod because the optical carriage travels further than the plate carriage in this embodiment of the invention in the ratio 1:(l1/N). The feed rod 253 is engaged at one end by a spring 251 and carries at its other end a roller 258 which engages a cam 259 adjustably mounted on the cam track 260 attached to the frame uprights 2H] and 2| I.

- The optical system is most clearly shown in Figs. 28, 29, 30 and 31. It comprises a prism box 26] mounted on the optical carriage and supporting the horizontal optical tube 262 and the vertical optical tube 263. The optical tube 262, which is conveniently made in telescopic sections, carries an extension 264 which is shown as of narrow rectangular shape, so as to cast as little shadow as possible, and it carries at its outer end a right angle prism 265 below which is mounted the downwardly facing telecentric lens 266. The telecentric lens is preferably provided with an adjustable mask device 261 similar to the mask arrangement shown in Fig. 16. The vertical optical tube 263 includes the mount 268 for the photographic lens 269 which may be of any suitable type of objective. Also mounted in the optical tube 263 is the shutter 210 which may be of anysuitable type and is-controlled by a cable release 21l in a manner to be described. At the upper end of the vertical optical tube may be placed an adjustable aperture plate 212 which is preferably similar in construction to that shown in Fig. 21. 'A light-tight loose flexible bag or bellows 213 extends from the end of the vertical optical tube to the plate carriage 2l8, so as to shield the lower side of the plate holder 220 from stray light. 4

Since the form of scanner now being described is designed to: operate with an erected image, a suitable image erecting system is provided. As illustrated, this comprises a set of prisms mounted in the prism box 261, and arranged in conjunction with the prism 265 to erect the image on the-plate. The prisms mounted in the prism box comprise an inverted right angled prism 214a with its axis extending transversely of the longitudinal axis of the horizontal optical tube and a smaller right angular prism 214b covering one-half of the horizontal face 215 of the prism 214a. The prism 2141) is in alignment with, but set in revers position to the prism 265. The path of the rays is as shown in Fig. 31, th rays coming up through the telecentric lens and prism 265 and being reflected by the latter to the prism 2141: which reflects the rays downwardly against one of the angular faces of the prism' 214a and thence across to the other angular face of said prism which reflects the rays upwardly through the horizontal surfac 215 of the prism and through the camera lens 269 to the plate. As a this prism arrangement results in erecting the image, the optical frame and carriage and optical system move faster than the platev frame and carriage, in the ratio l:(1-1/N), in accordance with the principle explained above. The system is equivalent to that indicated diagrammatically in Fig. '7.

The form of scanner shown in Figs. 23 to 33 is arranged to expose the plate only in one direction of movement of the frames. This is merely for mechanical convenience and increased accuracy, as already stated, but the scanner could be arranged to scan on both forwardand backward travels of the frames. When used as described, however, it is necessary to close the shutter during the reverse travel of the frames, and this is accomplished by means of the shutter cable release 21l, the end of which is connected to a reciprocating rod 216, Fig. 24, mounted to slide in a bracket 211 on the under side of the Plate frame member 2l4b. At the end of the frame release rod is a roller 218 adapted to engage a surface on the cam 250 which will act to open the shutter at the beginning of th scanning stroke. At the end of the scanning stroke the roller 218 engages a cam 219 which will trip and close the shutter.

The photographic scanning of a model of terrain under a projector presents a special problem because it is desired to photograph not only the model, but also the picture projected on the surface of themodel, and it is important to do this without having objectionabl shadows cast on the model by the optical tube carrying the telecentric lens. The elimination of shadows is taken care of when photographing under the Multiplex apparatus in the manner indicated in Fig. 32. In the Multiplex apparatus at least two projectors are used, Fig. 32 showing three projectors in position. In each of these projectors an aerial diapositive is placed, these diapositives representing, 

